1. Field of the Invention
This invention relates generally to a pressure sensitive plunger assembly for compressing a tube to obstruct the flow of fluid flowing through the tube and, more particularly, it relates to a pressure sensitive plunger assembly for compressing a tube to obstruct the flow of fluid flowing through the tube which measures the occlusion resistance pressure on the tube to reliably indicate full closure of the tube.
2. Description of the Prior Art
In the prior art, clamping devices for clamping resilient tubes to temporarily and periodically prevent fluid from flowing through the tube are well-known. Such clamping devices are often used in association with medical equipment, and are frequently used in connection with medical apparatus which perform circulation of fluids to or from a living body. Of course, clamping devices are also associated with a variety of other products in many different fields.
Clamping devices take various forms, but typically function by manually or electrically inducing engagement of a structure which pinches the tube at a particular location thereby reducing or completely preventing passage of fluid through the tube. Some clamping devices are connected to a mechanism for detecting a specific condition in the fluid which, when the condition occurs, activates the clamping or unclamping of the tube. For example, it may be desirable to terminate blood flow through a tube if the hematocrit level falls above or below a certain value. In this instance, if the hematocrit level drops, as sensed by a detection means, an electrical signal is relayed to the clamping device causing it to close off the tube. Similarly, it may be desirable to terminate blood flow through a tube on the detection of air entrained in the blood.
Many clamping devices currently in use are capable of accommodating only those flexible tubes having a small internal diameter (approximately one (1) millimeter to twelve and one-half (12.5) millimeters (approximately 1/2 inch)) and which are very pliable. Furthermore, many clamping devices currently in use maintain either a fully opened or a fully closed condition. That is, the tube positioned within the clamp may be either completely uncompressed (open tube) or completely compressed (closed tube), but can not be partially compressed. Such clamping devices do not provide incrementally increasing compression of the tube as required by some medical procedures. In addition, many clamping devices do not provide a mechanism for manually operating the clamping device under emergency situations, such as a power failure, or as may be dictated by medical necessity.
In an effort to overcome some of the shortcomings of the previous clamping structures, the Orth, U.S. Pat. No. 5,445,613, describes a clamping device having a clamping structure and a plunger. The plunger has a plunger end and a plunger shaft connected to the plunger end. The Orth patent's clamping device obstructs the flow of fluid through a tube by electrically or manually actuating the plunger end of the plunger against the tube in response to an electrical signal from a condition detection mechanism associated with the tube. The plunger of the clamping device of the Orth patent can also be actuated to compress the tube gradually, providing incrementally decreasing flow through the tube.
While the clamping device of the Orth patent obstructs the flow of fluid through a tube, there are several disadvantages with the Orth patent's clamping device. First, the clamping device of the Orth patent merely measures the positional displacement of the plunger relative to the clamping surface. Plunger position alone, however, is an unreliable analog for detecting full tube closure since there are many variables, i.e., tube size and valve positioning, which could cause the tube not to be fully occlude even when the plunger is at the "fully occluded" position. Furthermore, since the occlusion of the tube is directly related to the pressure generated by the rebound of the tube against the plunger, merely measuring the positional displacement of the tube greatly affects the accuracy of the clamping device on tubes having a variety of elasticities. The Orth patent's clamping device is not capable of measuring the occlusion pressure exerted by the plunger on the tube.
Second, the plunger shaft and the condition detection mechanism of the clamping device of the Orth patent are not sealed from the elements. Debris or the like entering into clamping device of the Orth Patent can adversely affect the movement of the plunger and/or the activation of the condition detection mechanism such that the clamping device fails to occlude the tube the proper amount.
Accordingly, there exists a need for a pressure sensitive plunger assembly for occluding a tube which can be used on variety of different tubes having a variety of different durometers. Additionally, a need exists for a pressure sensitive plunger assembly for occluding a tube which measures the amount of occlusion pressure exerted on the tube for reliably indicating full closure of the tube. Moreover, there exists a need for a pressure sensitive plunger assembly for occluding a tube which is sealed from the elements to inhibit debris and the like from entering within the plunger assembly and adversely affecting the operation of the plunger assembly.